Corrosion resistant electroplating process, and plated article

Abstract

To simplify manufacture of plated metal parts with high corrosion resistance especially suitable for use as sealing lids or cover elements for semiconductor packages, a substrate of Kovar, or Alloy 42, which are nickel-containing iron alloys, are electroplated with a base layer of a metal having an electromotive potential high with respect to that of the substrate, over which an intermediate layer is electroplated, which intermediate layer (16) has an electromotive potential which is low with respect to the base layer, and over that a cover layer (18) is plated which has an electromotive potential similar to that of the base layer. Suitable metals are gold-nickel-gold combinations, in which the gold layers should be over 10 microinches thick, preferably and in order to meet MIL-STD 883C, about 25 microinches thick. The intermediate layer (16), if of nickel, has an electromotive potential which is at the negative side of the electromotive series. Pin holes through the three layers may cause, under the influence of a corrosive atmosphere, migration of ions up to the base layer but, due to the arrangement of electromotive potentials of the intermediate and the cover layer, will not extend further so that the corroded substrate material will, effectively, form a plug for the pin hole and prevent progression of corrosion.

I claim: 
     
       1. A plated metal part comprising a substrate (12) of a metal which is corrodable in a corrosive or salt atmosphere environment; and   only three layers electroplated on said substrate, said only three layers comprising   a base layer (14) electroplated on the substrate and comprising a metal from the group consisting: of gold, platinum, silver, palladium, or their alloys;   a single intermediate layer (16) electroplated on the base layer (14) and comprising nickel or a nickel-based alloy; and   a cover layer (18) electroplated on the intermediate layer (16) and comprising a metal selected from the group consisting of: gold, silver, palladium, or their alloys.   
     
     
       2. The article of claim 1, wherein the base layer (14) and the cover layer (18), each, comprise gold. 
     
     
       3. The article of claim 2, wherein the gold layers have a thickness of over about 10 microinches; and the intermediate layer (16) has a thickness of between about 50 to 350 microinches.   
     
     
       4. A corrosion resistant plated metal part forming a substrate (12) comprising an iron-based alloy (F15), or alloy 42; and only three layers electroplated sequentially on said substrate to impart corrosion resistance to said substrate,   said only three layers comprising   a base layer (14) electroplated on the substrate (12) and comprising a metal selected from the group consisting of gold, platinum, silver, palladium, or their alloys;   a single intermediate layer (16) electroplated on the base layer (14) and comprising a nickel or nickel-based alloy; and   a cover layer (18) electroplated on the intermediate layer (16) and comprising a metal selected from the group consisting of gold, platinum, silver, palladium, or their alloys.   
     
     
       5. The article of claim 4, wherein said base layer (14) and said cover layer (18) comprise gold. 
     
     
       6. The article of claim 5, wherein the gold layers (14, 18) have a thickness of over about 10 microinches. 
     
     
       7. The article of claim 6, wherein the intermediate layer (16) has a thickness of between about 50-350 microinches. 
     
     
       8. The article of claim 5, wherein said base layer (14) has a thickness of about 25 microinches and said cover layer (18) has a thickness of at least about 25 microinches. 
     
     
       9. The article of claim 8, wherein said intermediate layer (16) has a thickness of at least about 150 microinches. 
     
     
       10. A corrosion resistant semiconductor package sealing cover comprising a substrate (12) comprising an iron-based alloy (F15), or alloy 42; and only three layers electroplated sequentially on said substrate to impart corrosion resistance to said substrate,   said only three layers comprising   a base layer (14) electroplated on a substrate (12) and comprising a metal selected from the group consisting of gold, platinum, silver, palladium, or their alloys;   a single intermediate layer (16) electroplated on the base layer (14) and comprising a nickel or nickel-based alloy; and   a cover layer (18) electroplated on the intermediate layer (16) and comprising a metal selected from the group consisting of gold, platinum, silver, palladium, or their alloys.   
     
     
       11. The sealing cover of claim 10, wherein the intermediate layer (16) has a thickness of between about 50 to 350 microinches. 
     
     
       12. The sealing cover of claim 10, wherein said base layer (14) and said cover layer (18) comprise gold. 
     
     
       13. The sealing cover of claim 12, wherein said gold layers (14, 18) have a thickness of about 25 microinches. 
     
     
       14. The sealing cover of claim 12, wherein the gold layers (14, 18) have a thickness of over about 10 microinches. 
     
     
       15. The sealing cover of claim 14, wherein the intermediate layer (16) has a thickness of between about 50 to 350 microinches. 
     
     
       16. The sealing cover of claim 12, wherein said base layer (14) has a thickness of about 25 microinches and said cover layer (18) has a thickness of at least about 25 microinches. 
     
     
       17. The sealing cover of claim 16, wherein the intermediate layer (16) has a thickness of at least about 150 microinches. 
     
     
       18. A process of plating a metal substrate (12) comprising an iron-based alloy F15 or alloy 42 to make the substrate corrosion-resistant, said process comprising the steps of   electroplating only three layers on said metal substrate, and   wherein the steps of electroplating said only three layers include electroplating, on said substrate (12) a first or base layer (14) which comprises a metal selected from the group consisting of: gold, platinum, silver, palladium, or their alloys;   electroplating, on said base layer (14) a single intermediate layer (16) which comprises a nickel or nickel-based alloy; and   electroplating on said single intermediate layer (16) a cover layer which comprises a metal selected from the group consisting of: gold, platinum, silver, palladium, or their alloys.   
     
     
       19. The process of claim 18, wherein said base layer (14) and said cover layer (18) comprise gold. 
     
     
       20. The process of claim 19, wherein said plating steps of plating the gold layers (14, 18) comprise plating said layers until they have a thickness of about 25 microinches. 
     
     
       21. The process of claim 19, wherein said plating steps of plating the gold layers (14, 18) comprise plating said layers until they have a thickness of over about 10 microinches. 
     
     
       22. The process of claim 21, wherein said plating step of plating the intermediate layer (16) comprise plating said intermediate layer until it has a thickness between about 50 to 350 microinches. 
     
     
       23. The process of claim 21, wherein the plating steps of plating said gold base layer (14) and said gold cover layer (18) comprise plating said gold layers until they have a thickness of over about 10 microinches; and wherein said plating step of plating said intermediate layer (16) comprises plating said intermediate layer until it has a thickness of about 150 microinches.   
     
     
       24. The process of claim 19, wherein said plating steps of plating the gold layers (14, 18) comprising plating said layers until said base layer (14) has a thickness of about 25 microinches and said cover layer (18) has a thickness of at least about 25 microinches. 
     
     
       25. The process of claim 24, wherein said plating step of plating the intermediate layer (16) comprises plating said intermediate layer until it has a thickness of about 150 microinches.